Method for producing mould and core through curing sodium silicate sand for casting by blowing

ABSTRACT

In a method for producing moulds and cores with cold box through curing sodium silicate sand for casting by blowing, a sand mixture for producing moulds and cores is filled into a forming tool by a core shooter or manually and then is shaped, and the operations of blowing, curing and stripping are carried out. Gases are sequentially blown in the order of CO 2  and compressed gas; or gases are sequentially blown in the order of compressed gas-CO 2 -compressed gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

The instant application is a continuation-in-part application of PCT international application No. PCT/CN2016/096655, filed on Aug. 25, 2016, which claims the benefit of the Chinese patent application No. CN201610143927.X filed on March 8, 2016 and CN201610296943.2 filed on May 6, 2016, the entire disclosures of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to the technical field of casting, and more particularly to a method for producing moulds and cores with cold box through curing sodium silicate sand for casting by blowing.

BACKGROUND

At present, the technology of producing moulds and cores by resin self-hardening sands, mainly including furan resin self-hardening sand, alkaline phenolic resin self-hardening sand, urethane resin self-hardening sand and Bonnie resin self-hardening sand, and the high-efficient core making processes, mainly including cold box resin sand core making process, hot box resin sand core making process and resin coated sand core making process, are widely used in casting production. In cold box resin sand core making process, gaseous amines are needed for curing the sand by blowing; as gaseous amines are toxic, irritating, inflammable and explosive, they have certain risks in production, transportation, storage and use. In hot box resin sand core making process and resin coated sand core making process, a forming tool need to be heated to 180-300° C., therefore the energy consumption is high, the smell is strong, and the working environment is poor. All the above-mentioned core making techniques require the use of synthetic organic resin as binder, whereas synthetic resin has complex production process and high cost and will release large amounts of toxic and odorous gases during core making and casting, which can pollute the environment and harm the health of workers.

The existing process of producing moulds and cores using inorganic binder is mainly the process of producing moulds and cores with cold box through curing sodium silicate sand for casting by blowing CO₂; the process of curing sodium silicate sand for casting by blowing CO₂ was invented by a Czech in 1948 and began to be popularized and applied in foundries in 1952. This process is still in use in many foundries now, however, the process of producing moulds and cores through curing sodium silicate sand for casting by blowing CO₂ has the following problems in application: over-blowing is easy to occur, the amount of added sodium silicate for casting is large, the mechanical properties of sand moulds and cores are low, it is necessary to increase the amount of added sodium silicate for casting in order to ensure sufficient processing properties of sodium silicate sand moulds and cores, the amount of added sodium silicate for casting is as large as 4%-8%, and the collapsibility is poor. Statistics show that for every 1% reduction in the amount of added sodium silicate for casting, the casting desanding man-hour is saved by 50%; when the amount of added sodium silicate for casting is 4%, the casting desanding man-hour is 25% of that when the amount of added sodium silicate for casting is 6%. It is the pursuit of foundry workers for several decades to solve the problem of sodium silicate sand over-blowing, improve the mechanical properties of sodium silicate sand and reduce the amount of added sodium silicate sand.

SUMMARY

The purpose of the present invention is to provide a method for producing moulds and cores through curing sodium silicate sand for casting by blowing on the premise of solving the problems that over-blowing is easy to occur, the amount of added sodium silicate for casting is large, and the mechanical properties of sand moulds and cores are low in the process of producing moulds and cores through curing sodium silicate sand for casting by blowing CO₂ in the prior art.

To achieve the above purpose, the present invention adopts the following technical solution:

A method for producing moulds and cores with cold box through curing sodium silicate sand for casting by blowing, in which a sand mixture for producing moulds and cores is filled into a forming tool by a core shooter or manually and then is shaped, and the operations of blowing, curing and stripping are carried out at room temperature; gases are sequentially blown in the order of CO₂ and compressed gas; or gases are sequentially blown in the order of compressed gas-CO₂-compressed gas.

The CO₂ is a gas mixture containing CO₂ or pure CO₂; wherein the content of CO₂ in the gas mixture is 40%-99%, and the rest is industrial nitrogen or dry air; this is favorable for guaranteeing the quality of moulds and cores and reducing the consumption of functional gas CO₂.

The compressed gas is composed of compressed air and/or compressed nitrogen. Furthermore, the compressed gas is compressed air or compressed nitrogen treated by dehumidification and having a dew point of lower than 5° C.; the water carrying capacity of the compressed gas is increased, and the mechanical properties of moulds and cores are improved.

The operation of blowing is to blow CO₂ first and compressed gas second, the gases are blown into the cavity of the forming tool for curing, the pressure for blowing CO₂ is 0.05-0.6 Mpa, and the blowing duration is 3-200 s; the pressure for blowing compressed gas is 0.05-0.7 Mpa, the blowing duration is 10-2400 s, and stripping is carried out after blowing is ended.

The operation of blowing is to blow CO₂ first and compressed gas second, the gases are blown into the cavity of the forming tool for curing, the pressure for blowing CO₂ is 0.05-0.4 Mpa, and the blowing duration is 10-60 s; the pressure for blowing compressed gas is 0.1-0.5 Mpa, the blowing duration is 20-200 s, and stripping is carried out after blowing is ended.

The operation of blowing is to blow compressed gas first into the cavity of the forming tool by a blow plate, the pressure for blowing compressed gas first is 0.01-0.4 Mpa, and the blowing duration is 5-600 s; then CO₂ is blown, the pressure for blowing CO₂ is 0.05-0.6 Mpa, and the blowing duration is 3-200 s; compressed gas is blown again after CO₂ blowing is ended, the blowing pressure is 0.05-0.7 Mpa, the blowing duration is 10-2400 s, and stripping is carried out after blowing is ended.

The operation of blowing is to blow compressed gas first into the cavity of the forming tool by a blow plate, the pressure for blowing compressed gas first is 0.03-0.3 Mpa, and the blowing duration is 5-120 s; then CO₂ is blown, the pressure for blowing CO₂ is 0.05-0.4 Mpa, and the blowing duration is 10-60 s; compressed gas is blown again after CO₂ blowing is ended, the blowing pressure is 0.1-0.5 Mpa, the blowing duration is 20-200 s, and stripping is carried out after blowing is ended.

Pulse blowing is adopted during the operation of blowing CO₂.

The sand mixture for producing moulds and cores is composed of raw materials with the following mass percentages: 1.2%-5.0% of sodium silicate for casting, 0.0%-2.5% of reinforcing agent, and the balance of raw sand.

The sand mixture for producing moulds and cores is composed of raw materials with the following mass percentages: 1.5%-3.0% of sodium silicate for casting, 0.0%-1.5% of reinforcing agent, and the balance of raw sand.

The sodium silicate for casting is CO₂-blowing cured sodium silicate, ester cured sodium silicate or VRH cured sodium silicate. The modulus of the sodium silicate for casting is 1.2-3.5, and is preferred to be 1.5-2.5.

The reinforcing agent is silica fume, zirconium fumed silica, precipitated silica, pyrogenic silica or fly ash, or a mixture of two or more of such materials.

The raw sand is foundry silica sand, spherical sand, zircon sand, forsterite sand or chromite sand. For moulds and cores produced by the present invention, mould assembling and pouring can be carried out after the moulds and cores are dried naturally by standing in workshop for 24 h and longer, and can also be carried out on the same day after the moulds and cores are dried by a surface drier.

Compared with the prior art, the present invention has the following advantages:

The present invention provides a method for producing moulds and cores with cold box through curing sodium silicate sand for casting by blowing, which can solve the problem of over-blowing in the method for blowing CO₂ into sodium silicate sand and reduce the amount of added sodium silicate by more than 50%; after reinforcing agent is added to sodium silicate sand mixture, the mechanical properties of the moulds and cores produced by the method for producing moulds and cores through curing sodium silicate sand for casting by blowing provided by the present invention can be improved by more than 100% compared with those produced by the method for blowing CO₂ into sodium silicate, sand cores and sand moulds have good collapsibility, sand in castings is easy to remove, and old sand can be reused; the gas evolution of moulds and cores is low, no toxic or odorous substance is produced during mould and core production, and the method can help to improve working conditions and is favorable for environmental protection.

DETAILED DESCRIPTION

The technical solution of the present invention will be clearly and fully described below in combination with the embodiments of the present invention. Apparently, the described embodiments are merely part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those ordinary skilled in the art without contributing creative labor will belong to the protection scope of the present invention.

In the method for producing moulds and cores with cold box through curing sodium silicate sand for casting by blowing at room temperature provided by the embodiments of the present invention, a sand mixture for producing moulds and cores is prepared by mixing raw sand, sodium silicate for casting and reinforcing agent with a sand mixer, then the sand mixture for producing moulds and cores is filled into a forming tool by a core shooter or manually and is shaped, CO₂ is blown first, compressed gas is blown second, the gases are blown into the cavity of the forming tool for curing, the pressure for blowing CO₂ is 0.05-0.6 Mpa, and the blowing duration is 3-200 s; the pressure for blowing compressed gas is 0.05-0.7 Mpa, the blowing duration is 10-2400 s, the lower limit of blowing duration is used for small moulds and cores, the blowing duration can be extended appropriately for large moulds and cores, and stripping is carried out after blowing is ended.

In the method for producing moulds and cores requiring high stripping strength, a sand mixture for producing moulds and cores is prepared by mixing raw sand, sodium silicate for casting and reinforcing agent with a sand mixer, then the sand mixture for producing moulds and cores is filled into a forming tool by a core shooter or manually and is shaped, gases are sequentially blown in the order of compressed gas-CO₂-compressed gas, compressed gas is blown first, the pressure is 0.01-0.4 Mpa, and the blowing duration is 5-600 s; the pressure for blowing CO₂ is 0.05-0.6 Mpa, and the blowing duration is 3-200 s; the pressure for blowing compressed gas again is 0.05-0.7 Mpa, the blowing duration is 10-2400 s, the lower limit of blowing duration is used for small moulds and cores, the blowing duration can be extended appropriately for large moulds and cores, and stripping is carried out after blowing is ended. This method of curing sand by blowing can make the stripping strength of moulds and cores high, and prevent moulds and cores from deformation and damage during stripping.

The moulds and cores can be dried naturally by standing in a room after stripping; and can also be dried rapidly by a hot pneumatic tube drier or a microwave drier.

The compressed gas is industrial compressed air or industrial nitrogen. The compressed gas is treated by dehumidification and is preferred to have a dew point of lower than 5° C.

In the embodiments of the present invention, the sand mixture for producing moulds and cores is composed of raw materials with the following mass percentages: 1.2%-5.0% of sodium silicate for casting, 0.0%-2.5% of amorphous silica, and the balance of raw sand. Preferably, the sand mixture for producing moulds and cores is composed of raw materials with the following mass percentages: 1.5%-3.0% of sodium silicate for casting, 0.0%-1.5% of amorphous silica, and the balance of raw sand.

In the embodiments of the present invention, the CO₂ used is a gas mixture of CO₂, nitrogen and air diluted by industrial nitrogen and dry air and containing 80% of CO₂, 60% of CO₂ or 40% of CO₂, and reference examples using industrial CO₂ containing 99.9% of CO₂ are given.

In the embodiments of the present invention, the raw sand is foundry silica sand, spherical sand, zircon sand or chromite sand. The sodium silicate for casting is CO₂-blowing cured sodium silicate, ester cured sodium silicate or VRH cured sodium silicate.

The reinforcing agent is silica fume, zirconium fumed silica, precipitated silica, pyrogenic silica or fly ash, or a mixture of two or more of such materials.

As a preferred manner in the embodiments of the present invention, pulse blowing is adopted during the operation of blowing CO₂.

In the embodiments of the present invention, the specific manner of filling the sand mixture for producing moulds and cores into the cavity of the forming tool by a core shooter for shaping is: using a cold box core shooter and a supporting forming tool to produce cores, filling the sand mixture for producing cores into a sand shooting cylinder of the core shooter after mixing, and shooting the sand mixture for producing cores into the cavity of the forming tool by the core shooter at a pressure of 0.4-0.7 Mpa.

In the embodiments of the present invention, the specific manner of filling the sand mixture for producing cores into the forming tool manually for shaping is: letting the sand mixture for producing moulds and cores flow continuously into the cavity of the forming tool through a hacking after mixing, stopping mixing when the amount of the sand mixture for producing moulds and cores is enough and 2%-5% in excess, starting a vibrating compaction machine, making the machine work for 15-30 s, and scrapping manually to remove excessive sand mixture for producing moulds and cores.

The high-efficient method for producing moulds and cores with cold box through curing sodium silicate sand by blowing provided by the embodiments of the present invention can solve the problem of over-blowing in the method for blowing CO₂ into sodium silicate sand and reduce the amount of added sodium silicate by more than 50%; meanwhile, the mechanical properties of the moulds and cores produced can be improved significantly, sand cores and sand moulds have good collapsibility, sand in castings is easy to remove, and old sand can be reused. Compared with resin core making process, the method of the present invention has the advantages that gas evolution is reduced by more than 90%, castings have relatively less air holes and crack defects, overall yield of casting is high, no toxic or odorous substance is produced during mould and core production, and the method can improve working conditions; as solid waste emission is relatively less, the method is favorable for environmental protection.

Embodiment 1

An MLWA1 cold box specimen machine manufactured by Suzhou Mingzhi Technology Co., Ltd. is used for producing cores. The composition of the mixture for producing cores is: 1000 g of Weichang washed-out sand, 30 g of ZS-2.9 sodium silicate for casting with a modulus of 2.85, and 3 g of zirconium fumed silica, which are well mixed by a laboratory bladed sand mixer; the sand mixture for producing cores is filled into a sand shooting cylinder and shot into the cavity of a standard 8-shaped specimen testing forming tool by compressed air at a pressure of 0.5 Mpa; the forming tool of core boxes drops with a main cylinder, a blow plate is pushed into the top of the forming tool, and the main cylinder rises and compresses the blow plate; a blowing valve is actuated, CO₂ is blown into the cavity of each sand core through the blow plate at a pressure of 0.15 Mpa, and pulse blowing is carried out by blowing gas for 3 s during each pulse, stopping for 5 s and completing three pulses; after blowing is ended, a scavenging valve is immediately actuated, a CO₂ pipeline is closed, compressed air is introduced to the blow plate of the forming tool, the compressed air is blown into the cavity of each sand core at a pressure of 0.2 Mpa, and the duration for blowing compressed air is 15 s; after blowing is ended, boxes are opened and cores are taken out; three sand cores are produced by each box, and 12 sand cores are produced by four boxes; the tensile strengths of 8-shaped specimens are tested by a hydraulic testing machine, instant strengths are tested in 60 s, and the average value of three specimens is taken; the final strengths of the specimens are tested after 24 h indoor standing. As tested, the instant tensile strengths are 0.16 Mpa, 0.14 Mpa and 0.15 Mpa, and the average value of the three specimens is 0.15 Mpa; the tensile strengths after 24 h are 1.2 Mpa, 1.1 Mpa and 1.3 Mpa, and the average value of the tensile strengths after 24 h of the three specimens is 1.2 Mpa.

Embodiment 2

An MLWA1 cold box specimen machine manufactured by Suzhou Mingzhi Technology Co., Ltd. is used for producing cores. The composition of the mixture for producing cores is: 1000 g of Dalin washed-out sand, 30 g of ZS-2.5 sodium silicate for casting with a modulus of 2.2, and 3 g of silica fume, which are well mixed by a laboratory bladed sand mixer; the sand mixture for producing cores is filled into a sand shooting cylinder and shot into the cavity of a standard 8-shaped specimen testing forming tool by compressed air at a pressure of 0.5 Mpa; the forming tool of core boxes drops with a main cylinder, a blow plate is pushed into the top of the forming tool, and the main cylinder rises and compresses the blow plate; a blowing valve is actuated, CO₂ is blown into the cavity of each sand core through the blow plate at a pressure of 0.1 Mpa, and the blowing duration is 15 s; after blowing is ended, a scavenging valve is immediately actuated, a CO₂ pipeline is closed, compressed air is introduced to the blow plate of the forming tool, the compressed air is blown into the cavity of each sand core at a pressure of 0.4 Mpa, and the duration for blowing compressed air is 25 s; after blowing is ended, boxes are opened and cores are taken out; three sand cores are produced by each box, and 12 sand cores are produced by four boxes; the tensile strengths of 8-shaped specimens are tested by a hydraulic testing machine, and instant strengths are tested in 60 s; the rest specimens are put into a 900 W Galanz microwave oven, the microwave oven is turned on, the specimens are baked for 3 min, and the strengths of the specimens after drying are tested. As tested, the instant tensile strengths are 0.18 Mpa, 0.17 Mpa and 0.19 Mpa, and the average of the three values is 0.18 Mpa; the tensile strength after 24 his 1.8 Mpa.

Embodiment 3

An MLWA1 cold box specimen machine manufactured by Suzhou Mingzhi Technology Co., Ltd. is used for producing cores. The composition of the mixture for producing cores is: 1000 g of Dalin washed-out sand, 20 g of ester cured sodium silicate HYT S-106 for casting, 2 g of silica fume, and 2 g of fly ash, which are well mixed by a laboratory bladed sand mixer; the sand mixture for producing cores is filled into a sand shooting cylinder and shot into the cavity of a standard 8-shaped specimen testing forming tool by compressed air at a pressure of 0.5 Mpa; the forming tool of core boxes drops with a main cylinder, a blow plate is pushed into the top of the forming tool, and the main cylinder rises and compresses the blow plate; a blowing valve is actuated, CO₂ is blown into the cavity of each sand core through the blow plate at a pressure of 0.18 Mpa, and pulse blowing is carried out by blowing gas for 3 s during each pulse, stopping for 5 s and completing three pulses; after blowing is ended, a scavenging valve is immediately actuated, a CO₂ pipeline is closed, compressed nitrogen is introduced to the blow plate of the forming tool, the compressed nitrogen is blown into the cavity of each sand core at a pressure of 0.4 Mpa, and the duration for blowing compressed nitrogen is 20 s; after blowing is ended, boxes are opened and cores are taken out; three sand cores are produced by each box, and 12 sand cores are produced by four boxes; the tensile strengths of 8-shaped specimens are tested by a hydraulic testing machine, instant strengths are tested in 60 s, and the average value of five specimens is taken; the rest specimens are put into a Type 101-1, 2000 W electric thermostatic drying oven and baked for 10 min at 120-150° C., the tensile strengths of the specimens after drying and cooling to room temperature are tested, and the average value of three specimens is taken. As tested, the instant tensile strengths are 0.19 Mpa, 0.25 Mpa and 0.22 Mpa, and the average value of the three specimens is 0.22

Mpa; the tensile strengths after 24 h are 1.7 Mpa, 1.8 Mpa and 1.8 Mpa, and the average value of the tensile strengths after 24 h of the three specimens is 1.77 Mpa.

The implementation methods of embodiment 4, embodiment 5, embodiment 6 and embodiment 7 are the same as that of embodiment 1 except that the varieties of raw sand and the amount of added sodium silicate for casting are different. Implementation conditions and results of embodiment 1, embodiment 2, embodiment 3, embodiment 4, embodiment 5, embodiment 6 and embodiment 7 are listed in Table 1.

TABLE 1 Amount of Amount added Amount of sodium of added Sodium silicate added Tensile raw silicate for silica strength Embodi- sand for casting fume Mpa ment Raw sand g casting g g Instant 24 h 1 Weichang 1000 ZS- 30 3 0.15 1.20 washed- 2.9 out sand 2 Dalin 1000 ZS- 30 3 0.18 1.80 washed- 2.5 out sand 3 Dalin 1000 HYT 20 4 0.22 1.75 scrubbed S-106 sand 4 Chromite 1000 HYT 15 3 0.22 1.60 sand S-106 5 Zircon 1000 HYT 15 3 0.23 1.65 sand S-106 6 Spherical 1000 HYT 15 3 0.24 1.75 sand S-106 7 Forsterite 1000 HYT 25 3 0.14 1.15 sand S-106

Embodiment 8

An MLWA1 specimen machine manufactured by Suzhou Mingzhi Technology Co., Ltd. is used for producing cores. The composition of the mixture for producing cores is: 1000 g of Weichang washed-out silica sand, 20 g of ester cured sodium silicate HYT S-106 for casting, and 3 g of zirconium fumed silica, which are well mixed by a laboratory bladed sand mixer; the sand mixture for producing cores is filled into a sand shooting cylinder and shot into the cavity of a standard 8-shaped specimen testing forming tool by compressed air at a pressure of 0.5 Mpa; the forming tool of core boxes drops with a main cylinder, a blow plate is pushed into the top of the forming tool, and the main cylinder rises and compresses the blow plate; a blowing valve is actuated, compressed air is blown into the cavity of each sand core through the blow plate at a pressure of 0.05 Mpa, and the blowing duration is 8 s; then CO₂ is blown into the cavity of each sand core through the blow plate at a pressure of 0.15 Mpa, and pulse blowing is carried out by blowing gas for 3 s during each pulse, stopping for 5 s and completing three pulses; after CO₂ blowing is ended, a scavenging valve is immediately actuated, a CO₂ pipeline is closed, compressed air is introduced to the blow plate of the forming tool, the compressed air is blown into the cavity of each sand core at a pressure of 0.2 Mpa, and the duration for blowing compressed air is 25 s; after blowing is ended, boxes are opened and cores are taken out; three sand cores are produced by each box, and 12 sand cores are produced by four boxes; the tensile strengths of 8-shaped specimens are tested by a hydraulic testing machine, instant strengths are tested in 60 s, and the average value of three specimens is taken; the final strengths of the specimens are tested after 24 h indoor standing, and the average value of three specimens is taken. As tested, the instant tensile strengths are 0.48 Mpa, 0.45 Mpa and 0.46 Mpa, and the average value of the three specimens is 0.46 Mpa; the tensile strengths after 24 h are 1.74 Mpa, 1.78 Mpa, 1.80 Mpa, and the average value of the tensile strengths after 24 h of the three specimens is 1.77 Mpa.

The compressed air is treated by a RD-1 SW refrigerant drier, and the dew point of the compressed air after treatment is 2-4° C.

The implementation methods of embodiment 9, embodiment 10 and embodiment 11 are the same as that of embodiment 8 except that the varieties of raw sand and the amount of added sodium silicate for casting are different, and implementation conditions and results are listed in Table 2.

TABLE 2 Amount Amount of of Amount added added of sodium zirco- added Sodium silicate nium Tensile raw silicate for fumed strength Raw sand for casting silica Mpa Embodiment sand g casting g g Instant 24 h 8 Weichang 1000 HYT S-106 20 3 0.46 1.78 washed-out silica sand 9 Chromite sand 1000 HYT S-106 15 3 0.42 1.70 10 Zircon sand 1000 HYT S-106 15 3 0.43 1.75 11 Spherical sand 1000 HYT S-106 15 3 0.56 1.85

Embodiment 12

The composition of the mixture for producing cores in this embodiment is: 40 kg of Weichang washed-out sand, 0.8 kg of ester cured sodium silicate HYT S-106 for casting, 0.08 kg of silica fume, and 0.08 kg of fly ash; the raw materials are put into a sand mixer successively, wherein the sand mixer is a 5206 cup-type sand mixer manufactured by Qingdao Fangxin Machinery Factory; the mixture for producing cores is obtained by mixing the raw materials for producing cores; then the mixture for producing cores is filled into boxes by artificial core making process and shaped, and the specific manner is: letting the sand mixture for producing cores flow continuously into boxes of 37 kg sand cores through a hacking, stopping mixing when the amount of the sand mixture for producing cores is enough and 2%-5% in excess, starting a vibrating compaction machine, making the machine work for 20 s, wherein the vibrating compaction machine is a XNZ29 vibrating compaction machine manufactured by Wuxi Xinan Foundry Machinery Co., Ltd., and scrapping the surface of each core print manually after vibrating; two blow pipes are inserted in the center of each sand core, CO₂ is blown into the cavity of each sand core through the blow pipes at a pressure of 0.2 Mpa, and pulse blowing is carried out by blowing gas for 5 s during each pulse, stopping for 5 s and completing four pulses; after blowing is ended, a scavenging valve is immediately actuated, a CO₂ pipeline is closed, compressed air is introduced, the compressed air is blown into the cavity of each sand core at a pressure of 0.2 Mpa, and the duration for blowing compressed air is 120 s; boxes are opened and cores are taken out with the help of a crane. The sand cores are placed in a core storage room and stand for 24 h or longer, and mould assembling and pouring can be carried out after the contained moisture is volatilized.

Nine standard 8-shaped specimens are prepared using 1 kg of sand mixture of embodiment 12 and the equipment of embodiment 1 through sand specimen preparing method and blowing curing method; the instant tensile strengths are tested, which are 0.16 Mpa, 0.15 Mpa and 0.17 Mpa, and the average value of the three specimens is 0.16 Mpa; the tensile strengths after 24 h are 1.3 Mpa, 1.5 Mpa and 1.4 Mpa, and the average value of the tensile strengths after 24 h of the three specimens is 1.4 Mpa.

Embodiment 13

The compressed air in this embodiment is treated by refrigeration dehumidification, and the dew point of the compressed air is 2-4° C.

The composition of the mixture for producing moulds in this embodiment is: 100 kg of Fujian sea sand, 2.0 kg of ester cured sodium silicate HYT S-106 for casting, 0.2 kg of zirconium fumed silica, and 0.2 kg of fly ash; the raw materials are put into a sand mixer successively and mixed for 30 s, wherein the sand mixer is a S20 cup-type sand mixer; the mixture for producing moulds is obtained by mixing the raw materials for producing moulds and filled into a sand box with a capacity of 190 kg through a sand bucket; another 100 kg of mixture for producing moulds is prepared according to the above composition and filled into another sand box with a capacity of 190 kg; a vibrating compaction machine is started and made to work for 25 s, wherein the vibrating compaction machine is a XNZ29 vibrating compaction machine manufactured by Wuxi Xinan Foundry Machinery Co., Ltd., and scrapping the surface of each sand box manually after vibrating. Curing is carried out by blowing with an instrument for curing sodium silicate sand by blowing of the utility model patent 201620231051.x; six blow pipes are uniformly distributed and inserted in the center of each sand mould; blowing process is set as that: compressed air is blown into the cavity of each sand mould at a pressure of 0.1 Mpa, and the blowing duration is 15 s; CO₂ is blown into the cavity of each sand core through the blow pipes at a pressure of 0.4 Mpa, and pulse blowing is carried out by blowing gas for 6 s during each pulse, stopping for 6 s and completing five pulses; after blowing is ended, a scavenging valve is immediately actuated, a CO₂ pipeline is closed, compressed air is introduced, the compressed air is blown into the cavity of each sand core at a pressure of 0.56 Mpa, and the duration for blowing compressed air is 600 s; moulds are taken out with the help of a crane. The sand moulds are placed in workshop and stand for 24 h or longer, and mould assembling and pouring can be carried out after the contained moisture is volatilized.

Nine standard 8-shaped specimens are prepared using 1 kg of sand mixture of embodiment 13 and the equipment of embodiment 1 through sand specimen preparing method and blowing curing method; the instant tensile strengths of three specimens are tested, which are 0.35 Mpa, 0.34 Mpa, 0.36 Mpa, and the average value of the instant tensile strengths of the three specimens is 0.35 Mpa; the tensile strengths after 24 h are 1.7 Mpa, 1.6 Mpa and 1.8 Mpa, and the average value of the tensile strengths after 24 h of the three specimens is 1.7 Mpa.

Reference Example 1

An MLWA1 cold box specimen machine manufactured by Suzhou Mingzhi Technology Co., Ltd. is used for producing cores. The composition of the mixture for producing cores is: 1000 g of Dalin washed-out sand, and 60 g of ZS-2.5 sodium silicate with a modulus of 2.4, which are well mixed by a laboratory bladed sand mixer; the sand mixture for producing cores is filled into a sand shooting cylinder and shot into a standard 8-shaped specimen testing forming tool by compressed air at a pressure of 0.5 Mpa; the forming tool of core boxes drops with a main cylinder, a blow plate is pushed into the top of the forming tool, and the main cylinder rises and compresses the blow plate; a blowing valve is actuated, CO₂ is blown into the cavity of each sand core through the blow plate at a pressure of 0.2 Mpa, and the blowing duration is 30 s; stripping is carried out after blowing is ended; three sand cores are produced by each box, and 12 sand cores are produced by four boxes; the tensile strengths of 8-shaped specimens are tested by a hydraulic testing machine, and the average value of three specimens is taken. As tested, the instant tensile strengths of five specimens are 0.16 Mpa, 0.13 Mpa and 0.16 Mpa, and the average value of the instant tensile strengths of the three specimens is 0.15 Mpa; the tensile strengths after 24 h are 0.50 Mpa, 0.54 Mpa and 0.52 Mpa, and the average value of the tensile strengths after 24 h of the three specimens is 0.52 Mpa.

Reference Example 2

An MLWA1 cold box specimen machine manufactured by Suzhou Mingzhi Technology Co., Ltd. is used for producing cores. The composition of the mixture for producing cores is: 1000 g of Dalin washed-out sand, and 30 g of ZS-2.5 sodium silicate with a modulus of 2.4, which are well mixed by a laboratory bladed sand mixer; the sand mixture for producing cores is filled into a sand shooting cylinder and shot into a standard 8-shaped specimen testing forming tool by compressed air at a pressure of 0.5 Mpa; the forming tool of core boxes drops with a main cylinder, a blow plate is pushed into the top of the forming tool, and the main cylinder rises and compresses the blow plate; a blowing valve is actuated, CO₂ is blown into the cavity of each sand core through the blow plate at a pressure of 0.2 Mpa, and the blowing duration is 15 s; after CO₂ blowing is ended, a scavenging valve is immediately actuated, a CO₂ pipeline is closed, compressed air is introduced to the blow plate of the forming tool, the compressed air is blown into the cavity of each sand core at a pressure of 0.4 Mpa, and the duration for blowing compressed air is 30 s; after blowing is ended, boxes are opened and cores are taken out; three sand cores are produced by each box, and 12 sand cores are produced by four boxes; the tensile strengths of 8-shaped specimens are tested by a hydraulic testing machine, instant strengths are tested in 60 s; the rest specimens are put into a 900 W Galanz microwave oven, the microwave oven is turned on, and stripping is carried out after blowing is ended; three sand cores are produced by each box, and 12 sand cores are produced by four boxes; the tensile strengths of 8-shaped specimens are tested by a hydraulic testing machine, and the average value of three specimens is taken. As tested, the instant tensile strengths of three specimens are 0.14 Mpa, 0.18 Mpa, 0.16 Mpa, and the average value of the instant tensile strengths of the three specimens is 0.16 Mpa; the tensile strengths after 24 h are 0.55 Mpa, 0.54 Mpa and 0.56 Mpa, and the average value of the tensile strengths after 24 h of the three specimens is 0.55 Mpa.

Reference Example 3

An MLWA1 cold box specimen machine manufactured by Suzhou Mingzhi Technology Co., Ltd. is used for producing cores. The composition of the mixture for producing cores is: 1000 g of Dalin washed-out sand, 20 g of ZS-2.5 sodium silicate with a modulus of 2.4, and 3 g of silica fume, which are well mixed by a laboratory bladed sand mixer; the sand mixture for producing cores is filled into a sand shooting cylinder and shot into a standard 8-shaped specimen testing forming tool by compressed air at a pressure of 0.5 Mpa; the forming tool of core boxes drops with a main cylinder, a blow plate is pushed into the top of the forming tool, and the main cylinder rises and compresses the blow plate; a blowing valve is actuated, CO₂ is blown into the cavity of each sand core through the blow plate at a pressure of 0.15 Mpa, and pulse blowing is carried out by blowing gas for 3 s during each pulse, stopping for 5 s and completing three pulses; after CO₂ blowing is ended, a scavenging valve is immediately actuated, a CO₂ pipeline is closed, compressed air is introduced to the blow plate of the forming tool, the compressed air is blown into the cavity of each sand core at a pressure of 0.2 Mpa, and the duration for blowing compressed air is 25 s; after blowing is ended, boxes are opened and cores are taken out; three sand cores are produced by each box, and 12 sand cores are produced by four boxes; the tensile strengths of 8-shaped specimens are tested by a hydraulic testing machine, and instant strengths are tested in 60 s; the rest specimens are placed in a room and stand for 24 h, the tensile strengths of 8-shaped specimens are tested by a hydraulic testing machine, and the average value of five specimens is taken. As tested, the instant tensile strengths of five specimens are 0.17 Mpa, 0.14 Mpa and 0.16 Mpa, and the average value of three specimens is 0.156 Mpa; the tensile strengths after 24 h are 1.7 Mpa, 1.6 Mpa and 1.8 Mpa, and the average value of the tensile strengths after 24 h of the three specimens is 1.7 Mpa.

Reference Example 4

CO₂ used in reference example 4 is a gas mixture diluted by industrial nitrogen and containing 80% of CO₂. Compressed air is treated by refrigeration dehumidification and has a dew point of 2-4° C.

An MLWA1 cold box specimen machine manufactured by Suzhou Mingzhi Technology Co., Ltd. is used for producing cores. The composition of the mixture for producing cores is: 1000 g of Dalin washed-out sand, 20 g of ZS-2.5 sodium silicate with a modulus of 2.4, and 3 g of silica fume, which are well mixed by a laboratory bladed sand mixer; the sand mixture for producing cores is filled into a sand shooting cylinder and shot into a standard 8-shaped specimen testing forming tool by compressed air at a pressure of 0.5 Mpa; the forming tool of core boxes drops with a main cylinder, a blow plate is pushed into the top of the forming tool, and the main cylinder rises and compresses the blow plate; a blowing valve is actuated, compressed air is blown into the cavity of each sand core through the blow plate at a pressure of 0.05 Mpa, and the blowing duration is 8 s; then CO₂ is blown into the cavity of each sand core through the blow plate at a pressure of 0.15 Mpa, and pulse blowing is carried out by blowing gas for 3 s during each pulse, stopping for 5 s and completing three pulses; after CO₂ blowing is ended, a scavenging valve is immediately actuated, a CO₂ pipeline is closed, compressed air is introduced to the blow plate of the forming tool, the compressed air is blown into the cavity of each sand core at a pressure of 0.2 Mpa, and the duration for blowing compressed air is 25 s; after blowing is ended, boxes are opened and cores are taken out; three sand cores are produced by each box, and 12 sand cores are produced by four boxes; the tensile strengths of 8-shaped specimens are tested by a hydraulic testing machine, instant strengths are tested in 60 s; the rest specimens are placed in a room and stand for 24 h, the tensile strengths of 8-shaped specimens are tested by a hydraulic testing machine, and the average value of three specimens is taken. As tested, the instant tensile strengths of three specimens are 0.35 Mpa, 0.34 Mpa and 0.36 Mpa, and the average value of the three specimens is 0.35 Mpa; the tensile strengths after 24 h are 1.7 Mpa, 1.62 Mpa and 1.83 Mpa, and the average value of the tensile strengths after 24 h of the three specimens is 1.73 Mpa. The mechanical properties of reference example 1, reference example 2, reference example 3 and reference example 4 are listed in Table 3.

CO₂ used in reference example 5 is a gas mixture diluted by industrial nitrogen and containing 60% of CO₂. CO₂ used in reference example 6 is a gas mixture diluted by industrial nitrogen and containing 40% of CO₂. Other implementation conditions are the same as those of reference example 4, and the implementation results of reference example 5 and reference example 6 are listed in Table 3.

TABLE 3 Amount of Amount Amount added of of sodium added added Sodium silicate re- Tensile raw silicate for inforcing strength Reference Raw sand for casting agent Mpa Concen- Example sand g casting g g Instant 24 h tration 1 Dalin 1000 ZS-2.5 60 0 0.15 0.52 CO₂ 99.9% washed- out silica sand 2 Dalin 1000 ZS-2.5 30 0 0.16 0.55 CO₂ 99.9% washed- out silica sand 3 Dalin 1000 ZS-2.5 20 3 g of 0.156 1.70 CO₂ 99.9% washed- silica out fume silica sand 4 Dalin 1000 ZS-2.5 20 3 g of 0.35 1.73 CO₂ 80% washed- silica out fume silica sand 5 Dalin 1000 ZS-2.5 20 3 g of 0.26 1.71 CO₂ 60% washed- silica out fume silica sand 6 Dalin 1000 ZS-2.5 20 3 g of 0.28 1.72 CO₂ 40% washed- silica out fume silica sand

Although preferred embodiments of the present invention are described, those skilled in the art can make additional alterations and amendments to the embodiments once knowing basic creative concepts. Therefore, the appended claims are interpreted to include the preferred embodiments and all the alterations and amendments which fall into the scope of the present invention.

Obviously, those skilled in the art could implement various modifications to and variations of the present invention without departing from the spirit and scope of the present invention. So, the present invention is intended to include the modifications and variations if the amendments and variations of the present invention belong to claims of the present invention and the equivalent technical scope. 

We claim:
 1. A method for producing mould and core with cold box through curing sodium silicate sand for casting by blowing, in which a sand mixture for producing mould and core is filled into a forming tool by a core shooter or manually and then is shaped, and the operations of blowing, curing and stripping are carried out; the method is characterized in that gases are sequentially blown in the order of CO₂ and compressed gas; or gases are sequentially blown in the order of compressed gas-CO₂-compressed gas; the compressed gas is composed of compressed air and/or compressed air and nitrogen treated by dehumidification and having a dew point of lower than 5° C.
 2. The method for producing mould and core with cold box through curing sodium silicate sand for casting by blowing according to claim 1, characterized in that the CO₂ is pure CO₂ or a gas mixture containing CO₂; wherein the content of CO₂ in the gas mixture containing CO₂ is 40%-99%, and the rest is industrial nitrogen or dry air.
 3. The method for producing mould and core with cold box through curing sodium silicate sand for casting by blowing according to claim 1, characterized in that the operation of blowing is to blow CO₂ first and compressed gas second, the gases are blown into the cavity of the forming tool for curing, the pressure for blowing CO₂ is 0.05-0.6 Mpa, and the blowing duration is 3-200 s; the pressure for blowing compressed gas is 0.05-0.7 Mpa, the blowing duration is 10-2400 s, and stripping is carried out after blowing is ended.
 4. The method for producing mould and core with cold box through curing sodium silicate sand for casting by blowing according to claim 3, characterized in that the operation of blowing is to blow CO₂ first and compressed gas second, the gases are blown into the cavity of the forming tool for curing, the pressure for blowing CO₂ is 0.05-0.4 Mpa, and the blowing duration is 10-60 s; the pressure for blowing compressed gas is 0.1-0.5 Mpa, the blowing duration is 20-200 s, and stripping is carried out after blowing is ended.
 5. The method for producing mould and core with cold box through curing sodium silicate sand for casting by blowing according to claim 1, characterized in that the operation of blowing is to blow compressed gas first into the cavity of the forming tool by a blow plate, the pressure for blowing compressed gas first is 0.01-0.4 Mpa, and the blowing duration is 5-600 s; then CO₂ is blown, the pressure for blowing CO₂ is 0.05-0.6 Mpa, and the blowing duration is 3-200 s; compressed gas is blown again after CO₂ blowing is ended, the blowing pressure is 0.05-0.7 Mpa, the blowing duration is 10-2400 s, and stripping is carried out after blowing is ended.
 6. The method for producing mould and core with cold box through curing sodium silicate sand for casting by blowing according to claim 5, characterized in that the operation of blowing is to blow compressed gas first into the cavity of the forming tool by a blow plate, the pressure for blowing compressed gas first is 0.03-0.3 Mpa, and the blowing duration is 5-120 s; then CO₂ is blown, the pressure for blowing CO₂ is 0.05-0.4 Mpa, and the blowing duration is 10-60 s; compressed gas is blown again after CO₂ blowing is ended, the blowing pressure is 0.1-0.5 Mpa, the blowing duration is 20-200 s, and stripping is carried out after blowing is ended.
 7. The method for producing mould and core with cold box through curing sodium silicate sand for casting by blowing according to claim 1, characterized in that pulse blowing is adopted during the operation of blowing CO₂.
 8. The method for producing mould and core through curing sodium silicate sand for casting by blowing according to claim 1, characterized in that the sand mixture for producing mould and core is composed of raw materials with the following mass percentages: 1.2%-5.0% of sodium silicate for casting, 0.0%-2.5% of reinforcing agent, and the balance of raw sand.
 9. The method for producing mould and core with cold box through curing sodium silicate sand for casting by blowing according to claim 1, characterized in that the sand mixture for producing mould and core is composed of raw materials with the following mass percentages: 1.5%-3.0% of sodium silicate for casting, 0.0%-1.5% of reinforcing agent, and the balance of raw sand.
 10. The method for producing mould and core with cold box through curing sodium silicate sand for casting by blowing according to claim 8, characterized in that the sand mixture for producing mould and core is composed of raw materials with the following mass percentages: 1.5%-3.0% of sodium silicate for casting, 0.0%-1.5% of reinforcing agent, and the balance of raw sand. 